1. Field of the Invention
This invention relates to methods of sound production and reproduction wherein it is desired to create an illusion of a desired apparent sound source distance from a listener.
2. Description of the Prior Art
Many cues are known that help to create the illusion of a sound source having a given apparent distance, but hitherto, no satisfactory means of simulating the illusion of sound source distance reliably has been known, although various means have been proposed and used to obtain a somewhat unreliable simulation of a distance effect.
Among cues that have been used are reproduced sound source loudness, reproduced sound source equalisation, reproduced ratio of direct to reverberant sound, and reproduced phase distortion.
It is found that in many rooms with good acoustics, it is possible for listeners to reliably discriminate the apparent distance of an actual sound source. Unpublished experiments-by James A. Moorer at Bell Labs in New Jersey, U.S.A. in the late 1970's showed that a convincing illusion of apparent sound source distance could be simulated by computing and reproducing the sounds of just five early reflections that would be produced in a computer-modelled room by an anechoically-recorded sound. Thus, in the prior art, it is known that simulation of actual or computed early reflections in a room can be used to simulate sound source distance effects.
However, in sound recording applications, the simulation of actual early room reflections has numerous problems, since each different sound source position and distance requires the computation of a new set of reflections, and one is confined to simulating position within a given simulated room with a given acoustical character. Simulating only a few reflections is liable to cause a sound with a high degree of comb-filter colouration, and when mixing a large number of sound sources, e.g. from a 48-track tape recorder, a very large amount of computation is required to simulate a different distance for each source, since each requires a different early reflection simulation.